Baculoviruses are highly virulent insect viruses that serve as biological control agents and as important expression vectors. As pathogenic insect viruses, baculoviruses serve as excellent model systems for studies of viral interactions with insect tissues and cells. Our studies have focused on the major envelope protein, GP64, of the budded virus particle. The GP64 protein appears to serve a number of functions in the infection cycle: 1) recognition of the host cell receptor molecules; 2) fusion of viral and host membranes during virus entry; and, 3) participation in budding or assembly of the virus.